Sheathed resistor electric heater



Nov. 17, 1953 A. c. 50668 SHEATHED RESISTOR ELECTRIC HEATER Filed No v 1, 1951 INVENTOR ALBEN C. 50665 ATTORNEY Patented Nov. 17, 1953 SHEATHED RESISTOR ELECTRIC HEATER Alben C. Boggs, Pittsburgh, Pa., assignor to Edwin L. Wiegand Company, Pittsburgh, Pa., a corporation of Pennsylvania Application November 1, 1951, Serial No. 254,289

2 Claims.

This invention pertains to a sheathed resistor electric heater, and to a method of making such heater.

More particularly, the invention pertains to a sheathed. resistor electric heater including a sheath having at least one opening therein, for example, a tubular sheath having one open end, a resistor element disposed in the sheath and having at least one end thereof accessible through the opening in this sheath, such resistor being embedded throughout substantially its length in an electric-insulating heat-conducting material, together with a terminal. for the sheathed resistor electric heater of a nature to provide a seal which will be effective to protect the resistor element and the embedding material against fluid or gases such as would have a deteriorating or adverse effect thereon.

That the refractory embedding material must be thoroughly dried and protected against moisture in order to preserve the insulating characteristics of the refractory material is Well known, and that the provision of a protective closure or seal has presented a considerable problem is evidenced by various prior patents such, for example, as the patent to Sutton, No. 1,992,787, which discloses the use of a vitreous material such as glass as a closure medium. Another patentee, Abbott, in Patent No. 1,770 824, proposes the use of a material such as Bakelite as the closure medium, and Charbonneau, et al., in Patent No. 2,489,998 proposes the use of a solid rubber plug which is inserted into the open end of a tubular sheath and then placed under longitudinal compression to distort at least one end of the rubber plug into engagement with the internal wall of the sheath and the external diameter of the terminal pin.

The use of vitreous or other material which hardens to become a substantially inflexible solid has several disadvantages, one of which is that the material used as the closure medium must have substantially the same coefficient of expansion and contraction as the material going to i ture to the refractory embedding material.

under pressure, and particularly when exposed to the efiect of fluids or gases, will generally acquire a permanent set and the sealing qualities will be destroyed.

In accordance with this invention, the refractory material is terminated short of the opening in the sheath to provide a pocket or chamber. To close the opening in the sheath and protect the refractory material from the deteriorating eliect of moisture, the pocket or chamber is filled with a preferably initially flowable partially cured or uncured rubber-like adherent material which is or becomes and remains elastic, and which material has the characteristic of expanding under the influence of heat as it cures or polymerizes into a rubbery elastic state. A cover or bushing, having an opening therein through which the terminal pin passes, covers the opening in the sheath in a manner to closely confine the sealing material within the pocket or chamber, and means are provided for maintaining the cover or bushing in close overlying relation with the opening in the sheath to thereby confine the rubber-like material within a predetermined area.

A moldable vulcanizable rubber or rubber-like material is then applied to the exterior of the sheath adjacent the opening therein in such manner as to surround the sheath and to com pletely cover the closure or bushing applied to the opening in the sheath, as Well as the protruding end of the terminal pin, an electric conduct ing wire attached to the terminal pin, and at least a portion of the length of the usual insulation which covers an electrical conducting wire. This rubber or rubber-like material is then shaped by the use of a mold and the application of heat to form the material into a continuous cover which is adhered to the exterior of the sheath adjacent the opening therein and to at least the leading end of the insulation for the electrical conducting wire, thereby closing the entire assembly against access of vapors or mois- The heat applied to the rubber or rubber-like exterior covering is conducted to the rubber-like material disposed in the pocket formed adjacent the opening in the sheath and serves to cure or polymerize such material into a flexible rubber-like state, simultaneously causing expansion of the material so that such material, being closely confined in the pocket, will expand into tight sealing engagement with the inner surfaces of the pocket and the external surfaces of the terminal pin extending through the pocket.

Various other objects and advantageous fea- 3 tures of the invention may be had from the fol lowing description when taken in conjunction with the accompanying drawings wherein:

Figure l is a fragmentary view, partly in elevation and partly in section, showing a terminal construction for a sheathed heater element embodying the ideas of this invention;

Figure 2 is a view similar to Figure 3 out with the heating element in cross-section to show the details thereof; and

Figure 3 is an elevation showing the cover or bushings forming a part of the terminal seal.

The heater shown in Figures 1 and 2' of the type commonly used for heating liquids, and comprises a resistor H designed for the passage of an electric current and the consequent generation of the desired heat, a t rminal pin [2 to which the end of the resistor element 5 I is suitably secured, a sheath l3 suitable to the tempera tures to be experienced, and commonly of metal, and refr ctcry material i4 embedding the r sistor H and the inner end of the pin 22 and serving both to electrically insulate resistor element and pin ano also to conduct heat from the resistor element to the sheath,

The heater element illustrated may be bent upon itself providing a body portion suitable to be inserted into the liquid to be heated, with the terminal portions thereof extending t rough opening in the wall of a tanl; or other vessel. It will be understood, however, that the heater e1ement may be of a single length, with one end Toe-- ing formed by a closed sheath and the opposite end including the terminal conne tion herein illustrated, and that the heater element ay be utilized for other purposes than the hea ing of liquids.

In the illustrated embodiment, the refractory material It is not extended to the end of the sheath [3, or is routed out short of the end sheath, to thereby rovide a pocket or chamber [5 adjacent the open. end of the sheath. The open end of the sheath is provided with a closure or bushing l8, preferably of ceramic or similar insulating material. In the embodiment here illustrated, the cover or bushing is provided with an axial bore ll and a shank it which extends into the pocket l5 at the open end of the sheath, the shank [B being externally smaller than the interior of the pocket and internally larger than the exterior oi the terminal pin 52. The axial bore I! may comprise successively different diameters IS and 2d and the lowermost end of the shank may be tapered in a direction from the terminal pin l2 toward the interior of the sheath as at 2i for purposes hereinafter made more clear.

Another element of the closure comp elastic material 22 filling the spaces bet-v. een the lower end of the shank l8 and the upper surface of the refractory material I-i, between the cuterior of the terminal pin l2 and the interior of the shank l8 and the outer diameter of the shank l8 and the interior walls of the pocket This material is formed in position, for example, by placing a proper quantity of the material in the pocket l5 within the sheath terminal portion and then applying the cov" or bushing l5}, forcing the shank 28 of the cover or bushing into the material, and thus forcing the material to flow upwardly into the spaces between the exterior of the terminal pin it and the interior of the shank l8, and between the exterior of the shank I8 and the walls of the pocket !5 in the sheath terminal portion. The different diameters of the axial bore in the cover or bushing, the lowermost diameter being the greater, provides for easier flow of the material between the exterior of the terminal pin l2 and the interior of the shank l8. and also provides for a greater amount of material immediately surrounding the terminal pin l2. The tapered portion ill at the lower end of the shank provides for a greater amount of the elastic material between the outer surface of the shank and the interior walls of the pocket I5,

thereby providing a greater insulating effect for the elastic material at this point.

For this method of application the material 22 must necessarily be in a plastic or flowable condition when it is first placed in the pocket or chamber 15, and the material 22 is such that it is or becomes and remains elastic and of a nature to adhere to the various surfaces with which it is in contact, and particularly to the exterior of the terminal pin 12, the walls of the pocket l5, and the interior and exterior of the shank IB. The material is also such that it expands during the curing or polymerization under the influence of eat, and since it is closely confined in the pocket 15 within a predetermined area, the material will be tightly pressed. against all surfaces defining the area. While the complete cause of such expansion of the material 22 on curing or polymerization under the influence of heat is not fully known, it might be assumed that the evolution of during at least the initial stages of curing or polymerization is responsible. Also, at least one stage of the curing or olymerization, the material assumes tacky state and closely adheres to the surfaces with which it is in contact.

As one example of a satisfactory material to orrn that of the closure indicated at 22, a table uncured or slow-curing silicone rubber. preferably having admixed therewith up to twice its weight or more of a substance suitable as a filler, may used. The preferred proportions of the admixture depend on such factors as the specific ingredient-.- and the specific a particular example being approxinaatv parts of the silicone rubl or known commercially as Silastic 120, and zircon ground to as this minus 400 mesh or finer.

The cover or bushing I 6 is held tightly in position in overlying relation win the open end of the sheath l3 in order to closely confine the material 2'2 within a predetermined area in the open end of the sheath whereby expansion of the ma terial 22 on curing or polymerization will press the material tightly against the surfaces and provide a very tight and effective seal. As illustrated in Figures 1 and 2 of the drawings, an electrical conducting wire 24 is secured to the terminal pin 12 by means of a deformable ring 25 which surrounds the conducting wire 2:3 and the terminal pin l2 and is crimped at 26 to secure the conducting wire 24 tightly on the terminal pin it. .The crimped connection between the conducting wire and the terminal pin is so positioned with respect to the cover or bushing that either the deformable ring or the end 2? of the conductor wire is pressed tightly against the cover or bushing 16 to hold it in position h respect to the open end of the sheath. It is to be understood that, if desired, other means such, for ex.- ample, as a nut threaded onto the terminal pin or a member staked on the terminal pin may be utilized to hold the cover or bushin IS in position. As is usual, the conductor wire 24 is provided throughout its major length with an insulating cover 23 which is in this instance preferably of rubber, or rubber-like material.

The closure for the open end of the sheath [3 comprises, as a third. element, a moldable material 29 which is capable of being molded about the end of the sheath [3 adjacent the open end thereof, the terminal pin i2 and conducting Wire 24, and about at least a portion of the length of the insulating material 28 surrounding the conducting wire 24. The material 253 is preferably such that it may be shaped by a mold and cured or polymerized into a flexible elastic covering by being subjected to heat, and also such that the material will vulcanize into tight sealing engagement with the exterior surface of the end of the sheath l3 and with the insulating covering 28 on the conducting wire 25.

As one example, an uncured. rubber-like material Which is capable of flowing under heat and pressure may be applied to the end of the sheath I3, the protruding end of the terminal pin l2 and the conductor wire 24 connected thereto, and the insulating material 28 in the form of a tube, with the material being such that when it is placed in a mold and subjected to heat the material will fiow in a manner to closely engage all of the parts within the tube and will assume a tight sealing engagement therewith.

The material 22 disposed in the pocket formed at the end of the sheath is capable of being cured or polymerized by the use of the heater due to the transfer of heat from the resistor element H through the terminal pin l2 and the sheath [3, as well as the refractory material It, which is effective on the material 22. However, with the construction herein disclosed wherein the outer surface of the open end of the sheath, the protruding end of the terminal pin and at least a portion of the insulated length of the conducting Wire 24 is covered by a flexible sheath formed of a material which is ilowable and vulcanizable under heat and pressure, the heat supplied to the material 29 to cause the same to flow and vulcanize Will simultaneously be effective to cure or polymerize the material 22, thereby forming two flexible, elastic seals simultaneously.

With the construction herein disclosed, and the method of forming a sealed terminal for a sheath embedded-resistor electric heater, there is provided a terminal having numerous advantageous features. For example, an inner and an outer sealing means is provided, both of which are flexible, and both of which will be effective to resist contamination of the refractory material With moisture or vapors. The invention herein disclosed is particularly advantageous for use as, for example, a refrigerator defroster, or in other places where the terminal portion of the heater element would be subjected to vapors, gases, and moisture.

What is claimed is:

1. An electric heating element comprising a hollow sheath having an opening therein, a resistance conductor member disposed within said sheath and having a terminal end projecting through said sheath opening, a refractory heat conducting material within said sheath for electrically insulating said conductor member and its terminal end from said sheath, an insulated conductor wire having an exposed end electrically connected to the terminal end of said resistance conductor, and a molded protective covering of insulating material enclosing said electrical connection and in hermetically sealed engagement with the defining surface of adjoining parts of said sheath and the insulated end of said Wire whereby to restrict foreign material from entering around said protective covering and affecting the operation of said heating element.

2. An electric heating element comprising a hollow sheath having an opening therein, a resistance conductor member disposed within said sheath, a terminal pin disposed within said sheath and projecting at its outer end through said opening, the inner end of said pin being electrically connected to said conductor member, a refractory heat conducting material Within said sheath for electrically insulating said conductor member and said terminal pin from said sheath, an insulated conductor wire having an exposed end electrically connected to the end of said terminal pin adjacent said sheath opening, and a protective covering of insulating material molded and vulcanized about and completely enclosing said electrical connection and bonded in hermetically sealing relation to the adjacent insulated end of said wire, said protective covering also extending over and bonded in hermetically sealing relation with the defining surface of an adjoining part of said sheath.

ALBEN G. BOGGS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,087,736 Pugh July 20, 1937 2,379,942 Webber July 10, 1945 2,460,795 Warrick Feb. 1, 1949 2,489,998 Charbonneau et a1. Nov. 29, 1949 2,570,800 Hamm Oct. 9, 1951 FOREIGN PATENTS Number Country Date 557,765 Great Britain Dec. 3, 1943 

